1. Field of the Invention
The invention relates to a device for homogenizing, mixing and/or pelletizing chemical substances comprising of at least one component by means of an extruder which exhibits several casing sections, at least one endless screw, a die arrangement and at least one cutting mechanism.
2. State of the Art
Certain pellets of chemical substances, in particular additives, require a high production rate. Since these chemical substances frequently consist of components with the most varied of physical properties (melting point, water content, melting viscosity, miscibility, adhesiveness, etc.), difficulties are encountered during pelletization, in particular at a high throughput. For example, the extruder develops undesired deposits, the dies become clogged, thereby making pelletization more difficult or no longer possible. In addition, the individual components can exhibit varying behavior while being fed in.
Known in the art from DE 38 32 006 A1 is an extruder for pelletizing a molding material and the use of such an extruder. The extruder makes it possible to achieve a uniform distribution of the molding material to be processed over the entire cross section of the forming plate.
DE 39 34 592 describes a perforated plate for pelletizing plastic strands. The perforated plate is designed in such a way as to prevent deposits and associated product contamination.
DE 42 93 549 A1 discloses the fabrication of compacted, superficially sticky pellets as well as the device suitable for executing the process. This process is intended to prevent the pellets from baking on and adhering to the inner wall of the pelletizing shaft, even at very high throughputs and without limiting the range of formulations.
Therefore, the object of the invention is to propose a device of the aforementioned type which enables an optimal homogenization and mixing of the extrusion mass on the one hand, and a uniform pelletization with the desired pellet properties on the other, both at the highest possible throughput.
According to the invention, the object is achieved by virtue of the fact that the extruder exhibits at least one opening for metering purposes, and that the extruder casing and/or individual die sections are thermally decoupled and separately heatable and/or coolable.
Since the different starting materials have varying temperature properties, it is necessary to set a specific temperature profile throughout the entire extrusion process. In this case, high temperature jumps may become necessary, which are then achieved via the thermal decouplings and ability to heat and/or cool the individual extruder casing sections. The extrusion process often starts out at a high temperature, with a low temperature at the extruder output. A specific endless screw configuration can also help bring about a good result.
To achieve a uniform distribution of the extrusion mass, the extrusion strand is shaped into a ring before entering the die arrangement, with the diameter of the ring-shaped stand increasing toward the die arrangement. In this case, a uniform pressure distribution is in place in front of the dies.
In addition, the invention provides for the use of eccentric dies, in particular during stand pelletization.
The extrusion strand divided into individual die strands can be broken down in an advantageous manner by means of a cutting mechanism located directly in back of the die arrangement or to the side of the extruder.
Additional preferred features and combinations thereof are outlined in the subclaims and following descriptions to the figures.